Phenotypic Characterization of Non-Fermentative Gram Negative Bacilli from Clinical Samples

Author Name(s): *Kiran. R, Dr. P. K. Uma Maheswari, Dr. Radha Madhavan, Mr. Abhishek Routray
Author Email:


This is a prospective study conducted in the SRM Medical College Hospital and Research Centre, Tamil Nadu from April 2010 to July 2010 to find out the prevalence of NFGNB in the clinical specimens and to isolate and identify the prevalent NFGNB from different clinical samples received in SRM medical college laboratory. Confirmation of the isolates is done by various biochemical reactions and antimicrobial susceptibility testing with special reference to Pseudomonas as per CLSI guidelines. Different samples were collected, processed as per standard test and antimicrobial susceptibility tests were performed. Most of the Pseudomonas spp. shows drug resistance. Therefore it is recommended that the above sensitivity pattern should be confirmed by Minimum Inhibitory Concentration. Of the 2129 specimen obtained, 99 isolates were NFGNB and among those Pseudomonas (64%) was more prevalent, followed by Acinetobacter (19%), NFGNB (10%) and Moraxella (6%). Antimicrobial susceptibility test, with reference to pseudomonas shows 68% – 70% susceptibility to Aminoglycosides, 34% resistance to Ciprofloxacin. 16% resistance to Imipenem, 72% resistance to Meropenem and cefepime and Aztronam were 100%. Polymixin B (100%) and Colistin (98%) were sensitive. Both Imipenem and Meropenem sensitive were 28%, Imipenem sensitive, Meropenem sensitive 58%, both Imipenem and Meropenem resistant were 14%.


The non-fermentative gram negative bacilli are groups of aerobic, non-sporing bacilli that either do not use carbohydrates as a source of energy or degrade them through metabolic pathways other than fermentation. Non fermenting gram negative bacteria were considered to be non pathogenic and commensal of little significance. Recently there has been a tremendous interest in these organisms as they are being isolated from clinical specimens with increasing frequency.
Pseudomonas aeruginosa and Acinetobacter baumannii are the common non-fermentative gram-negative bacteria found that have minimal nutritional requirements and can survive on a wide variety of surfaces and in aqueous environments. They rarely cause serious infections in otherwise healthy persons and are infrequently identified as normal microbial flora in healthy individuals, but they are of greatest concern in hospitalized patients, particularly those in intensive-care units (ICUs), where these opportunistic pathogens are capable of causing severe invasive infections in critically ill and immunocompromised patients such as bacteremia, pneumonia, urinary tract infection, meningitis, endocarditis, burn wound infection, eye infection, surgical site infection and osteomyelitis. Recent advances in medicine such as the advent of more elaborate surgery and intensive care, the use of immunosuppressive drugs, the availability of the invasive procedures or instrumentation and the increase in number of immuno-compromised patients liable to nosocomial infections with these NFGNBs are on rise. Increase in concern to treat these infections due to NFGNBs as they possesses intrinsic mechanisms of resistance to various groups.


The study highlights or emphasizes the importance to look for, identify various NFGNBs in the hospital environment as well as clinical specimens recovered in the microbiology laboratory. The identification of isolates can be enhanced by using automated systems. Packaged systems can be recommended, provided one understands their shortcomings and is willing to setup supplemental tests to identify weakly reactive or fastidious strain. The isolation of NFGNBs was more in ICU settings which warrants routine surveillance of ICU to keep in check, these NFGNBs. Patterns of susceptibility and resistance of the isolates recovered in SRM Medical College Hospital & Research Centre, India during the study period was found to be in par with the observations of various studies conducted across national and international institutions. The study suggests the physicians the judicious use of Imipenem and Meropenem and also opt Piperacillin/Tazobactum as the drug of choice therefore of low level of resistance. No resistance was observed to Polymyxin B, because of lack of utility of Polymyxin B for therapy, which can be saved for future use for life threatening mortality associated infections. Identification of MBL producers in these nosocomial isolates is essential, since MBL producing isolates are associated with a high level of mortality especially in immunocompromised patients particularly in ICU setting.

781 total views, 2 views today

Download PDF File

About the author: tej